Friction clutch with low disengaging force

ABSTRACT

A friction clutch for a motor vehicle having a clutching friction member and clutching mechanism with a cover and a clutch thrust plate. A resilient clutch member and disengaging gear is disposed between the rear surface of the thrust plate and the cover for moving the clutch thrust plate towards the cover. The clutch is provided with a wear adjustment device, a resilient servo member and a resilient smooth engagement member. The resilient servo member is mounted outside the clutching friction member. The load pressure feature combining the load pressure features of the resilient servo member and smooth engagement member globally follows the load pressure feature of an axially operating resilient clutching member.

The present invention concerns friction clutches with low declutchingforce, notably for motor vehicles.

DESCRIPTION OF THE RELATED ART

As is known, in a conventional clutch interposed between input shaft andan output shaft, a diaphragm bears on the bottom of a cover, fixed to aflywheel driving in rotation, in order to move a thrust plate in thedirection of the said flywheel, forming a reaction plate, in order togrip the friction linings of a clutch friction member between the saidthrust and reaction plates.

The driving flywheel is fixed to a first shaft, such as an input shaft,whilst the clutch friction member has at its inner periphery a hub forfixing it, with respect to rotation, to a second shaft, such as anoutput shaft.

The clutch is therefore normally engaged, or clutched, with transmissionof torque between the input and output shafts.

In order to disengage, or declutch, the clutch, it is necessary, bymeans of a clutch release bearing, to act axially by pushing, in thecase of a clutch of the pushed type, on the inner end of the fingers ofthe diaphragm in order to cause the said diaphragm to pivot and tocancel out the force exerted by this diaphragm on the axially movablethrust plate in order to release the friction linings. The torque isthen no longer transmitted from the input shaft to the output shaftsince the friction linings are no longer gripped between the thrust andreaction plates fixed to the cover with respect to rotation.

Normally, the cover, the thrust plate and the diaphragm form a unitaryassembly referred to as a clutch mechanism which is attached by itscover to the flywheel, elastic tongues connecting the thrust plate tothe cover with respect to rotation, with axial mobility.

The diaphragm, as is known, has a central hole and has an outerperipheral part in the form of a Belleville washer extended inwards by acentral part divided into radial fingers by slots. This diagram, throughits Bellville washer part, bears on the cover and on the thrust plate.Thus the declutching device of the clutch, which makes it possible tocounteract the action of the clutching elastic means at will, is formedby the fingers of the diaphragm on the inner end of which the clutchrelease bearing acts, whilst the Bellville washer of the diaphragmconstitutes axially acting clutching elastic means for gripping thefriction linings between the thrust and reaction plates and therefore toact axially on the thrust plate in the opposite direction to the bottomof the cover.

In the free state, this diaphragm has a frustoconical form. Once mountedin the clutch, its Bellville washer is mounted under prestressing and ismore or less flattened. During the operation of declutching, ordisengaging, the clutch, the clonicity of its Bellville washer ismodified.

As is known, the characteristic curve of this diaphragm, whichrepresents the force exerted as a function of the movement, for examplereferred to the level of the inner end of the diaphragm fingers, isdetermined by the dimensions of its Bellville washer, notably by theratio between the height of the truncated cone of the Bellville washerin the free state and the thickness of the diaphragm.

This characteristic curve passes through a maximum.

Thus the force to be exerted on the inner end of the diaphragm fingersincreases up to a maximum, gradually decreases to a minimum, and thenincreases once again. The difference between the maximum and minimum canbe great. For more information on this characteristic curve, referenceshould be made for example to the documents FR-A-1 392 569 and WO 97/19275.

In the document FR-A-1 392 569, an elastic progressive action device wasprovided to avoid passing through the aforementioned maximum during thedeclutching travel. This device is mounted in series with the Bellvillewasher of the diaphragm and has an elastic force appreciably less thanthat of the Bellville washer. This device has a limited travel between aprestressed position where its force is at a maximum and a stressedposition where its force is at a minimum.

With this arrangement, a declutching force is obtained which isincreasing overall at the clutch release bearing.

During the declutching travel it is not possible to obtain as great anassistance as desired, the progressive action device reducing the loadexerted by the diaphragm on the thrust plate during declutching.

The load curves of the progressive action device, when it is mountedwithin the friction member, and of the diaphragm, have shapes which donot make it possible to combine them in order to obtain high assistancefor declutching, in particular if it is wished to respect declutchingtravels and forces compatible with the current declutching controls.Moreover, the shape of the curve of the progressive action devicechanges, notably because of phenomena of encrustation of the frictionlinings, very rapidly with the life of the clutch, and the higher theassistance level required, the more this cancels out the assistance fordeclutching. In order to prevent ageing of the curve of the assistancedevice, it is preferable to place the latter at a point where itsstiffness curve will remain stable over time and, in particular, at apoint placed outside the progressive action zone of the friction memberwhere the lining contact and the phenomenon of encrustation change andcause the progressive action curve to change.

It can then be considered using an assistance spring.

Thus, in the certificate of addition 86 983 to French patent 1 392 569,it has already been proposed to interpose, between the elastic washer ofthe diaphragm and the thrust plate, an auxiliary elastic washer, thesaid two elastic washers being placed in series; the auxiliary elasticwasher allows a certain amount of progressiveness in the engagement ofthe clutch and procures a certain degree of assistance force during itsdisengagement.

In the document U.S. Pat. No. 5,186,298, a friction clutch including adevice for taking up wear and a progressive action device mounted withinthe friction member has already been proposed; in the document FR-A-2684 151, a clutch of the same type has already been proposed in whichthe load curves of the progressive action device and of the diaphragmare combined in order to obtain high assistance on declutching;unfortunately, for the reasons indicated above, such an arrangement isnot suitable.

SUMMARY OF THE INVENTION

The object of the present invention is to create, simply andeconomically, a friction clutch equipped with a device for taking upwear and a progressive action device mounted within the friction member,with a low declutching force, having recourse to springs acting inseries without appreciably decreasing, throughout the life of theclutch, the force for gripping the friction linings in the state withthe clutch engaged.

Thus, according to the invention, a friction clutch, notably for motorvehicles, has a clutch friction member and a clutching mechanism havinga cover with a transversely oriented bottom and fixing means for fixingthe clutching mechanism to a flywheel driving in rotation, a thrustplate having at the front a friction face for cooperating with theclutch friction member, elastic tongues for connecting the thrust platewith the cover with respect to rotation, with axial mobility, and,interposed between the back face of the thrust plate and the bottom ofthe cover, on the one hand axially acting elastic clutching meansaxially forcing the thrust plate in the opposite direction to the bottomof the cover and on the other hand a declutching device forcounteracting the action of the said elastic clutching means as requiredand moving the thrust plate in the direction of the bottom of the coverover a so-called plate lifting distance, the clutching mechanism beingequipped with a device for taking up wear on at least one of the liningsof the clutch friction member and elastic assistance means for assistingthe declutching force, elastic progressive action means being mountedwithin the clutch friction member and acting axially only on a travel ofthe thrust plate, is characterised by the fact that the elasticassistance means are mounted outside the clutch friction member and theload/compression characteristic combining the load/compressioncharacteristics of the elastic assistance and progressive action meansfollows overall the load/compression characteristic of the axiallyacting elastic clutching means.

This is the difference between these two characteristics which representthe change in the force to be supplied in order to declutch the clutch;this may be low, since these characteristics may be close to each other;it may be constant if these are parallel, one following another towithin a constant; it may be slightly increasing when they are notstrictly parallel.

The progressive action device mounted within the friction member enablesthe latter, or more exactly the linings carried by the latter, to adaptgeometrically to the friction faces of the reaction plate and pressureplate which, notably, under the effect of temperature rises due tofriction, deform, the most usual deformation being adopting a coneshape; by virtue of the progressive action device, the friction liningsfollow these deformations whilst adapting to them, so that wear on thesaid linings is reduced. It is however important to note that thesedeformations do not have a very great amplitude axially, and aprogressive action device tolerating an adaptation of the frictionlinings of three to four tenths of a millimeter, measured axially, issufficient; thus, for a lifting of the thrust plate of around 1.2millimeters, it can be seen that the progressive action device acts atmost only when one side of this lifting has taken place. Naturally, thisdepends on the application.

The aim of the invention is also to take advantage of this finding:advantageously, the elastic progressive action means act axially onlyover a travel of the thrust plate which is at least equal to one thirdof the lifting of the plate.

By virtue of this arrangement, there is less risk of the contribution ofthe progressive action means to the assistance force interfering withthe value of the latter in use.

Advantageously, the elastic clutching means and the elastic assistancemeans each consist of a Belleville washer, the two Belleville washersbeing mounted in series and placed axially between the thrust plate andthe bottom of the cover.

Preferably, the first Belleville washer is referred to as the negativeBelleville washer, its load supplied decreasing when the height of itstruncated cone decreases, and the second Belleville washer is referredto as the positive Belleville washer, its load supplied increasing whenthe height of its truncated cone decreases.

Advantageously, the thrust plate has at its rear an abutment situatedradially below the stop zones in order to limit the inclination of thefirst Belleville washer and prevent it turning.

Preferably, force transmission means are interposed between the innerperipheries of the first and second Belleville washers.

Advantageously, the Belleville washers are kept in contact with theforce transmission means by an elastic clamp, optionally divided, cominginto engagement with the external faces of the Belleville washers.

According to one embodiment, the declutching device is annular in shapeand the two Belleville washers are mounted in series between the thrustplate and a manoeuvring stop carried by the declutching device which ismounted at its outer periphery so as to pivot on a primary stop carriedby the bottom of the cover radially above the manoeuvring stop, itselflocated radially above a secondary stop carried by the bottom of thecover; the device for taking up wear having ramp means with rampsdisposed circumferentially and stop zones, the first Belleville washeris in contact at its outer periphery with the stop zones, whilst thesecond Belleville washer bears at its outer periphery on the manoeuvringstop, the said washers being inclined in opposite directions; thedeclutching device has a peripheral part of annular shape extended by amain part divided into radial fingers by slots; the manoeuvring stop isformed by stamping and is connected to the inner periphery of theannular peripheral part of the declutching device by a dished partdirected axially in the opposite direction to the manoeuvring stop; theperipheral part of the declutching device is offset axially with respectto its main part; the primary stop is offset axially with respect to thesecondary stop.

Advantageously, the force transmission means consist of a spring ring.

According to another embodiment, the device for taking up wear havingramp means with ramps disposed circumferentially and stop zones, thefirst Belleville washer is in contact with the stop zones, whist thesecond Belleville washer bears on the cover; preferably, the firstwasher is in contact through its outer periphery with the stop zoneswhist the second washer bears through its outer periphery on the cover;the force transmission means are carried by the declutching device.

As a variant, the first washer is in contact through its median partwith the stop zones whilst the second washer bears through its innerperiphery on the cover.

According to another variant the first washer is in contact with thestop zones through its inner periphery whilst the second washer bears onthe cover through its inner periphery.

Advantageously, the bottom of the cover carries an abutment for limitingthe inclination of the second Belleville washer.

Preferably, the second elastic washer is the outer peripheral part of adiaphragm extended inwards by a central part divided into radial fingersby slots.

According to one embodiment, the declutching device comprises atransverse plate carrying at its outer periphery the force transmissionmeans and connected by its inner periphery to a sleeve mounted so as toslide axially.

According to another embodiment, the declutching device comprises anannular disc carrying in its radially median part the force transmissionmeans and having, at its outer periphery, lugs passing through openingsformed in a cylindrical peripheral skirt on the cover, the lugs on theannular disc being adapted to bear on an edge of these openings when theadjacent part of its inner periphery of the annular disc is movedaxially.

According to yet another embodiment, the declutching device comprises adisc having an annular part extended towards the axis by a central partdivided into radial fingers by slots, the force transmission means beingplaced at the outer periphery of the said annular part, itself mountedso as to be articulated on the inner periphery of the bottom of thecover.

Advantageously, the device for taking up wear is actuated by the elasticclutching means.

According to another variant, the device for taking up wear is actuatedby the force transmission means.

The description which follows illustrates the invention with regard theaccompanying drawings in which;

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a half view in axial section of a clutch according to theinvention in the clutch engaged position;

FIGS. 2 and 3 are views similar to FIG. 1 showing a variant clutchaccording to the invention;

FIG. 4 is a view showing another variant clutch according to theinvention;

FIG. 5 is a view showing yet another variant clutch according to theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The clutch of the pushed type depicted in FIG. 1 is of the typedescribed in the French patent application filed on Sep. 6, 1996 underthe number 96 11 009, the description of which is to be considered asforming part of it. Overall, such a clutch includes a set of parts ofannular shape, namely in axial succession a flywheel 1 for driving inrotation, for fixing the clutch to a first shaft, such as an inputshaft, a clutch friction member 2 having at its outer periphery frictionlinings 20, 21 and at its inner periphery a hub 22 for connecting theclutch in rotation with a second shaft, such as an output shaft, athrust plate 3, a first Belleville washer 4, a stop spring ring 5, asecond Belleville washer 6 inclined in the opposite direction comparedwith the first Belleville washer 4, a declutching device 7 of annularshape, a cover 8 of annular shape having a bottom 80 overall oftransverse orientation with a central hole and at its outer peripheryfixing means 81 for fixing the cover 8 to the flywheel 1 forming areaction plate.

The flywheel 1 has at its rear a friction face 10 and is depicted herepartially, knowing that, in a known fashion, it has holes centrally forfixing it to the input shaft by means of screws. Here, the flywheel 1 ismade in a single piece, whilst being made of castable material, justlike the thrust plate 3 having at its front a friction face 30 facingthe friction face 10 of the flywheel 1. The flywheel 1 and thrust plateare here made of cast iron or any other material suited to dry friction.

The clutch friction member 2 has a support disc 23 for carrying thefriction linings 20, 21, optionally divided. These linings 20, 21 extendon each side of the support disc 23 whilst being fixed to it for exampleby riveting. Here the linings 20, 21 are fixed by bonding or brazing tothe metallic support disc 23.

Axially acting elastic progressive action means 24 are interposedbetween the two linings 20, 21 for progressive clamping thereof betweenthe flywheel 1 and thrust plate 3. These means can have any appropriateshape. Here these means 24 are produced by shaping the support disc 23.This disc, non-limitatively, can have a central part for connecting it,elastically or not, to the hub 22, and a peripheral part divided intoradial blades for example of the tripod type. Each blade then has acentral bearing zone intended for fixing one of the friction linings 20,21 and two outer peripheral bearing zones intended to cooperate with theother one of the friction linings 21, 20.

The bearing zones are offset axially with respect to the central part ofthe disc 23, the central bearing zone, of large extent, being connectedto the said central part by a tangential fold, whilst the peripheralbearing zones are connected to the said central bearing zone by obliquefolds. For more information, reference should be made to the documentU.S. Pat. No. 5,452,783, also showing an embodiment with frictionlinings divided into studs. In this way the phenomena of encrustation ofthe linings 20, 21 in the blades are minimised. Thus the elasticprogressive action means are more stable over time.

As mentioned above, the disc 23 can be coupled elastically to the hub22. As a variant, the disc 23 is coupled rigidly to the hub 22, theflywheel 1 then being divided so as to have two masses coupledelastically to each other by circumferentially or radially actingsprings.

As a variant, the flywheel 1 can be in two parts and have a supportflange fixed at its inner periphery to the input shaft and at its outerperiphery to a reaction plate having the friction face 10. The cover 8can then be connected to the flywheel 1 in two parts by means of axiallyoriented lugs issuing from its cylindrical peripheral skirt 82. Theselugs, in the form of tenons, are then engaged in mortises formed at theouter periphery of the reaction plate or of the support flange. The freesection of the lugs, forming the aforementioned fixing means 81 of thecover 8, can be fixed by crimping, folding over or welding to the flangeor to the reaction plate, as described for example in the French patentapplication 95 12523 filed on Oct. 24, 1995 and published under thenumber FR-A-2 741 917.

Here the cover 8 has a conventional form and the fixing means 81consists of a radial shoulder on the cover 8, directed radially in theopposite direction to the axial axis of symmetry of the clutch, the saidshoulder 81 being provided with holes, not visible, for mountingmembers, such as screws or as a variant rivets, for fixing the shoulder81 to the flywheel 1.

Where it is a case of an application to a motor vehicle, the input shaftis here the drive shaft of the vehicle on the crankshaft of which theflywheel 1 is fixed, whilst the output shaft consists of the input shaftof the gear box depicted partially at 100 in FIG. 1.

Naturally, it is possible to reverse the structures, the first shaftbeing able to be an output shaft and the second shaft an input shaft.

The thrust plate 3 is connected in rotation with the hollow-shaped cover8 by elastic tongues, not visible in the figure, enabling the thrustplate 3 to move axially with respect to the cover 8. The thrust plate 3is therefore fixed with respect to rotation to the cover 8 and flywheel1, whilst being axially movable with respect to them.

Here the outer cylindrical skirt 82 of the cover 8, connecting thebottom 80 to the radial fixing shoulder 81, has holes locally for thepassage of lugs, which the thrust plate 3 has in radial projection. Thetangential elastic tongues are fixed at one of their ends to the lugsand at their other end to a radial area 83 on the cover. These elastictongues are distributed regularly on the circumference, in a knownfashion; their number, like that of the lugs, depends on theapplication, knowing that, for private cars, generally three groups ofelastic tongues are used. As a variant, the tongues can be inclined orof radial orientation. In all cases, they exert an axially orientedrestoring force.

The fixing thereof to the areas 83 and the lugs is achieved by means offixing members, usually rivets, or as a variant screws or bolts.

The first Belleville washer 4, adjacent to the thrust plate 3, bears atits outer periphery on bearing zones 114 described below.

This washer 4 is inclined in the direction of the cover 8, its concavitybeing directed towards the thrust plate 3.

The second Belleville washer 6, adjacent to the declutching device,bears at its outer periphery on the declutching device 7 which, for thispurpose, has an annular stop 73. The second Belleville washer 6 isinclined in the direction of the thrust plate 3, in the oppositedirection to the first washer 4, its concavity being directed towardsthe bottom 80 of the cover 8.

The two Belleville washers 4 and 6 thus have a V-shaped in crosssection, whilst being in contact at their inner periphery with theannular force transmission spring ring 5 interposed between them.

More precisely, under the conditions described below, one of theBelleville washers provides the clamping of the clutch and is designatedbelow as the clamping washer; the other Belleville washer providesassistance for declutching and is designated below as assistance washer.

The clamping washer, like the Belleville washer part of a diaphragm, issuch that the load which it procures increases with the height of thetruncated cone which it represents; the assistance washer is such thatthe load which it procures decreases with the height of its truncatedcone; the two washers working in the area of their practically linearload/compression characteristic curve, it is seen that, by choosingwashers whose curves are, in these areas, practically parallel, thedeclutching force, which at each position of the declutching device isequal, or proportional, to the difference between the loads of thewashers, is small and practically constant; as a variant, if thestiffness of the clamping washer is greater than that of the assistancewasher, it is possible to obtain a declutching force which is low butincreasing slightly with the declutching travel. These characteristiccurves here take account of the force due to the elastic progressiveaction means 24 of the friction member 2, and theoretically of the forcedue to the elastic tongues, but the latter is negligible, these forces,as is known, acting in the direction of the declutching andparticipating in the assistance for declutching. For more information,reference should be made to the document WO 97/19 275, and notably toFIG. 4 where the variation in clonicity of a Belleville washer isdepicted.

Thus the positive washer has an area of use which, considering thecharacteristic curve of a diaphragm is situated originally overall atthe maximum of the said curve, whilst the area of use of the negativeBelleville washer is situated beyond the said maximum, as mentioned inthe document WO 97/19 275.

The stop 73 of the declutching device 7 constitutes a manoeuvring stopas described below.

Here, the declutching device 7 is metallic and the stop 73 is producedby stamping, being of rounded shape.

These Belleville washers 4, 6 are of course dimensioned so that anequilibrium is produced in combination with the elastic progressiveaction means 24 when the clutch is in the engaged position, the positiondepicted in FIG. 1.

Advantageously, the washers 4, 6 are hollowed locally, here by forming,in order to receive the spring ring 5. The outer face of these washers4, 6 is grooved in order to hold a U-shaped clamp 50, the free ends ofwhose arms are of axial orientation. The clamp 50 extends by its bottomradially below the washers 4, 6.

The clamp 50, here of annular shape, is elastic and elastically clampsthe washers in contact with the spring ring 5 whilst being in contactthrough its arms with its outer face of the said washers. This clamp 50can as a variant be divided into clips. According to the inclination ofthe washers 4, 6, the clamp opens or closes.

The declutching device 7, here metallic, is able to bear locally at itsouter periphery on an annular-shaped primary stop 71 formed by stampingat the outer periphery of the bottom 80 of the cover 8, here made ofstamped metal sheet. This cover 8 has, at the inner periphery of itsbottom 80, with a central hole, a secondary stop 72 of annular shapeformed by stamping.

The declutching device 7 is able to come locally in contact on thisprimary stop 71 forming a pivoting stop. The primary stop 71 is offsetaxially in the direction of the shoulder 81 and of the thrust plate 3with respect to the secondary stop 72.

Thus, in the clutch engaged position, the declutching device 7 bears onthe secondary stop 72. The manoeuvring stop 73 of the declutching deviceis located radially between the primary 71 and secondary 72 stops.Naturally, the stops 71 to 73 can be replaced by annular spring rings,the cover 8 and the declutching device 7 then being hollowed for thispurpose.

In all cases, the stops 71 to 73 are carried respectively by the bottom80 of the cover 8 and the declutching device 7.

It will noted that the outer periphery 75 of the declutching device 7 isoffset axially with respect to the main part 76 of the said declutchingdevice 7 in order, in combination with the offset of the primary stop71, to reduce the axial dimension. This offset of the peripheral part 75is produced by locally dishing the declutching device 7 at 74, in thedirection of the bottom 80 of the cover. This dishing 74 connects theperipheral part 75 to the manoeuvring stop 73 so that the peripheralpart 75 is connected to the main part 76 by an annular portion roughlyin the shape of a reversed S. It will be noted that the dish 74 alsomakes it possible to radially hold and centre the second washer 6. Thedish 74 is directed axially in the reverse direction compared with themanoeuvring stop 73 and stiffens the area lying between the manoeuvringstop 73 and the peripheral part 75 of the declutching device 7.

All this is possible since the declutching device 7 does not appreciablyexert any elastic action axially, its load being low.

In order to ensure perfect consistency of the clamping force, theclutching mechanism is equipped with a device for taking up wear such asthe device 90; the device 90 was described in detail in the Frenchpatent application filed on Sep. 17, 1996 under the number 96 11 297, towhich reference should be made for more information, and thecorresponding description should be considered to form part of thepresent application; its constitution will simply be repeated.

The device for taking up wear 90 comprises circumferentially disposedramp means 111 consisting of an annulus made of cutout sheet metal anddished so as to exhibit circumferentially disposed ramps; the saidannulus also has stop zones as 114 consisting of the rounded top edge ofdishes in the form of arcs of a circle centred on the axis of the clutchand here placed radially towards the outside with respect to the ramps.

The thrust plate 3 has, here moulded in one piece, on its face turnedtowards the bottom of the cover 8, studs 104 distributedcircumferentially at a distance from each other which corresponds tothat which circumferentially separates two successive ramps, the studs104 being intended each to cooperate with a ramp.

The ramp means 111 are placed axially between the first washer 4 and thethrust plate 3 so that the studs 104 receive the ramps and the firstwasher 4 cooperates with the stop zones 114 which thus constitute thestop means by means of which the washers 4 and 6 act on the thrust plate3.

One of the stop zones 114 of the ramp means 111 is extended at its outerperiphery by a shoulder parallel to the axis of the clutch ending in atransverse return, that is to say extending in a plane perpendicular tothe axis of the clutch, provided at its periphery with a set of teeth118.

The device for taking up wear 90 also comprises a ratchet wheel 120 withinclined teeth fixed to a shaft which also carries a worm 113; thethread and pitch of the worm 113 are adapted to the set of teeth 118 ofthe ramp means 111.

The axis of the ratchet wheel 120 is carried rotatably by a support 112,made of sheet metal cut out and folded, in the shape of a U having a weband two flanges intended to support the shaft.

The support 112 is extended externally in L-shaped arms each terminatingin a C-shaped end 130 by means of which the support 112 is fixed to thecover by crimping to the edges of a transverse opening 106 formed in thetransverse wall in of the cover 2.

The support 112 is adapted to receive an elastic member 131 in thegeneral shape of a crosshead, each end of which is provided with aninward return; more precisely, the longer part of the crosshead carriesa control tongue 135 at its end; the shorter part of the crosshead has areturn 136, known as a non-return pawl, which extends roughly parallelto the control tongue 135 whilst being at a distance from it so that,when the elastic member 131 and ratchet wheel 120 are mounted in thesupport 112, the non-return pawl 136 and control tongue 135 eachcooperate with a tooth root, the two teeth concerned here beingpractically diametrally opposed.

A helical compression spring is placed between the ratchet wheel 120 andsupport arm 112, whilst being coiled around the shaft; the worm 13 andratchet wheel 20 are cut from the same piece.

The helical spring constitutes the elastic taking-up means; the ratchetwheel 120 is in line with the non-return pawl 136 which, by cooperationwith the inclined teeth 121 on the ratchet wheel 120, prevents theratchet wheel 120, and the worm 113, from turning in the anti-clockwisedirection, as seen in the figure.

The support 112, carrying the ratchet wheel 120, the worm 113 and thehelical spring, being fixed to the cover 8, the first washer 4 moveswith respect to it during declutching and reclutching operations; thefirst washer 4 carries at its periphery a radial appendage referred toas an actuator 145 extending radially outwards in order to cooperatewith the elastic member 131; it will be understood that, by virtue ofthis arrangement, when the first washer 4 tilts during declutching andreclutching operations, the actuator 145 moves from right to left, asseen in the figure, the control tongue 135 which, by cooperation withthe teeth 121 on the ratchet wheel 120, causes the ratchet wheel 120 torotate in the clockwise direction; when the actuator 145, in return, ismoved to the right, the elasticity of the tongue 135 of the elasticmember 131 and the inclination of the teeth 121 mean that this tongue135 moves to the right whilst climbing the teeth 121, which are heldfixed in rotation by the non-return pawl 136.

The device for taking up play which has just been briefly describedfunctions as explained in the application cited above; by virtue of thetaking-up device 90, the two washers 4 and 6 retain the same position,in the clutch engaged position, whatever the wear on the linings 20, 21.

The declutching device 7 is designed to counteract and overcome asrequired the elastic action of the Belleville washers 4, 6 with a viewto releasing as required the friction linings 20, 21 of the clutchfriction member 2 from between the thrust plate 3 and the reaction plateconsisting of the flywheel 1 in order to disengage the clutch.

The Belleville washers 4, 6 and the elastic progressive action means 24make it possible to grip the said linings between the plates 1, 3, theBelleville washer 4, or clamping washer, constituting axially actingclutching means forcing the thrust plate 3 in the opposite direction tothe bottom 80, roughly of transverse orientation, of the cover 8. Thebottom 80 is directed radially towards the axial axis of symmetry X—X ofthe clutch.

The clutch is here of the pushed type. It is therefore necessary to actby pushing in the direction of the arrow F on the inner end of the mainpart 76, with central hole, of the declutching device 7 by means of aclutch release bearing 200 carried here by the casing of the gearbox.

Thus, in FIG. 1, the clutch is in the engaged position (linings 20, 21gripped between the plates 1, 3).

In the clutch engaged position, the declutching device 7 is in contactwith the secondary stop 72 (zero clearance), whilst, during thedeclutching travel, the clearance between the device 7 and stop 72increases, the declutching device 7 pivoting about the primary stop 71.

More precisely, the first Belleville washer 4, adjacent to the thrustplate 3, is the negative clamping washer, that is to say, when theheight of the truncated cone (or total thickness) of the washerdecreases, the load supplied by the washer decreases.

The Belleville washer adjacent to the declutching device 7 is thepositive or assistance washer. Thus, when the height of the truncatedcone of the washer decreases, the load supplied by the washer increases,as can be seen in FIG. 4 of the document WO 97/19 275. This positivewasher 6 has a preponderant action with respect to the negativeBelleville washer 4. It is adapted to deform the latter, that is to sayto flatten it. Its maximum developed load is for example greater inabsolute value than the maximum load developed by the negativeBelleville washer 4. Here the stiffness of the positive washer 6 ishigher than the stiffness of the negative washer 4 in absolute value.According to the invention, the load/compression characteristiccombining the characteristics of the assistance washer 6 and the elasticprogressive action means 24 roughly follows the characteristic of theclamping washer 4.

The spring ring 5 transmits the forces between the washers 4, 6.

The declutching device 7 has a main part 76 in the form of fingersseparated by slots, this main part 76 extending the peripheral parts 75.

These fingers have a greater length than the fingers of a conventionaldiaphragm. They can be ribbed longitudinally centrally.

The peripheral part 75 connects the fingers together and consists of asimple washer advantageously provided with blind radial slots openingout towards the outside so that this washer exerts no load or a verysmall load.

In this way it is possible to obtain large lever arms and reduce theload to be applied at 77 (the contact line of the clutch releasebearing) in order to disengage the clutch.

The fingers of the main part 76 have a long length compared with theheight of the washer 75, for example the height of the washer 75 and ofthe dishes 73, 74 can be such that the distance between the primary stop71 and actuating stop 73 is one tenth of the distance between theprimary stop 71 and the stop 77 for the clutch release bearing.

In the clutch engaged position, the position of the manoeuvring stop 73is fixed since the lever constituting the declutching device 7 is inabutment on the primary 71 and secondary 72 stops of the cover 8. Thesecondary stop 72 therefore makes it possible to define a referenceposition for the declutching device 7.

The ends of the fingers 76 of the declutching device 7 therefore alwaysoccupy the same position whatever the wear on the friction linings 20,21 and or the friction faces 10, 30.

In this position, the elastic progressive action means 24 are compressedto the maximum extent. It will be noted that the main part 76 has a foldfor reducing the axial dimension.

During the declutching operation, by pushing axially by means of theclutch release bearing 200 at 77 on the inner end of the fingers of themain part 76, the declutching device 7 leaves its secondary stop 72 anda clearance appears. The manoeuvring stop 73 tends to move closer to thestop zones 114. The distance between the stop zones 114 and themanoeuvring stop 73 tends to decrease. The positive washer 6 opens,whilst the negative washer 4 closes again and the elastic progressiveaction means 24 relax.

Because of the stiffnesses of the washers 4, 6 and the elasticprogressive action means 24, a new equilibrium is created with reductionof the load exerted by the Belleville washers on the thrust plate, the Vdefined by the Belleville washers 4, 6 closing up.

When the clutch release bearing 200 has effected its maximum travel, theclearance between the secondary stop 72 and the device 7 increases. Thefirst negative Belleville washer 4 closes again, the height of itstruncated cone decreases, whilst the second positive Belleville washer 6opens, the height of its truncated cone increasing.

The loads of the two washers 4, 6 decrease greatly because the firstwasher 4 is negative and the second washer 6 positive.

These washers then being greatly off-load, the elastic tangentialtongues then ensuring a return of the thrust plate 3 towards the bottom80 of the cover 8. A clearance therefore appears between the thrustplate 3 and the linings 20, 21.

It will be noted that an annular abutment 32 is formed on the back face36 of the thrust plate 2, here by moulding. This abutment 32 preventsthe first Belleville washer 4 from turning, which would cause anincrease in the load exerted on the thrust plate 3, and an unbalancingor even re-engagement of the clutch. Thus anti-turning means areassociated with the first Belleville washer 4, which consequently ismounted under prestressing.

Naturally, for safety reasons, an abutment can be provided for limitingthe travel of the declutching device 7 so as to prevent the secondwasher 6 coming under load again because the first washer 4 is incontent with the stop 32.

Thus the declutching device 7 can carry small columns passing throughopenings formed in the bottom 80 of the cover 8. The head of the smallcolumns then comes into contact with the face of the bottom 80 turned inthe opposite direction to the thrust plate 3.

In the clutch engaged position, the declutching device 7 always has thesame position whatever the degree of wear on the friction linings and/orfriction faces.

As will have been understood, the spring ring 5 constitutes a forcetransmission means of rounded shape. As a variant, this spring ring canbe replaced by a rounded dish formed at the inner periphery of one ofthe Belleville washers 4, 6.

This dish has for example a shape similar to that of the stops 71 to 73.The force transmission means can therefore have different shapes.

The thrust plate 3 has at its front a friction face 30 for cooperatingwith the clutch friction member 2. The rear face of the thrust plate,directed axially towards the bottom 80 of the cover 8, is shaped so asto form an abutment 32 limiting the inclination of the negativeBelleville washer 4.

This abutment 32, obtained by casting, is located radially underneaththe stop zones 114, having a height less than these.

The Belleville washers 4, 6, the device for taking up wear 90 and thedeclutching device 7 are interposed between the cover 8 and thrust plate3 in order to form with these a manipulatable and transportable unitaryassembly referred to as the clutching mechanism. It is this clutchingmechanism which is fixed to the flywheel for driving in rotation 2.

As a variant, the washer 75 can be given a small degree of elasticity inorder to improve comfort at the pedal controlling the clutch releasebearing and to exert a return action.

More stiffness can be given to the positive Belleville washer 6 byincreasing for example its thickness compared with the negativeBelleville washer 4. It is possible to act on the angle of the truncatedcone of the Belleville washers 4 and 6 or any other means so that thepositive Belleville washer 6 is preponderant. The two Belleville washers4 and 6 can be conventional Belleville washers or Belleville washershaving fingers at their inner and/or outer periphery, according to thecharacteristics required for each application.

The positive Belleville washer 6 can be replaced by any other washerhaving a similar linear characteristic. Thus the positive washer 6 canbe an axially acting corrugated washer. The definition positiveBelleville washer therefore encompasses this type of variant.

The clutches depicted partially in FIGS. 2 to 5 are of the type depictedin FIGS. 1 to 4 of the French patent application filed on Apr. 7, 1997under the number 97 04 214, the corresponding description of which formspart of the application.

According to the variant in FIGS. 2 and 3, the declutching device 7comprises a transverse plate 41 carrying at its outer periphery theannular force transmission spring ring 5; the transverse plate 41 isconnected by its inner periphery to a sleeve 42 mounted so as to slideaxially.

This declutching device 7 is designed to counteract and overcome asrequired the elastic action of the Belleville washers 4 and 6 with aview to releasing as required the friction linings 20, 21 and the clutchfriction member 2 from between the thrust plate 3 and reaction plate 4in order to disengage the clutch.

The sleeve 42 of the declutching device 7 can be moved, for the purposeof the declutching operation, in one direction or the other, that is tosay in the direction of the arrow F, the clutch being of the pulledtype, or in the opposite direction to that of the arrow F, the clutchbeing of the pushed type: this depends on the choice of the relativecharacteristics of the first 4 and second 6 Belleville washers.

FIG. 2 shows the case of a pushed clutch, that is to say declutching isobtained by acting, at the sleeve 42, in the opposite direction to thatof the arrow F; the second Belleville washer 6 is here the positive orassistance washer and the first washer 4 is the negative or clampingwasher.

In FIG. 2, the clutch is shown engaged under the load of the secondBelleville washer 6, transmitted to the thrust plate 3, via the forcetransmission means 5, here in the form of a spring ring, by the firstBelleville washer 4 in abutment through its outer periphery on the stopzones 114 and through its inner periphery on the annular abutment 32.

When there is an action on the sleeve 42 in the opposite direction tothat of the arrow F, the positive washer 6 is in some way compressed,its exerted load increasing and its inner periphery being brought closerto the bottom 80 of the cover 8; this compression is assisted by theclamping washer 4, which releases the energy stored, in the engagedposition, under the effect of the preponderant positive washer 6, duringthe clutching operation. The compression travel of the positive washer 6is limited at the declutching device 7 or, as depicted, by a dish 86 onthe bottom 80 of the cover 6 with which the positive washer 6 comes tocooperate at the end of the declutching operation.

It will easily be understood that, in order to produce a clutch of thepushed type, that is to say in which the declutching operation isobtained by acting on the sleeve 42 in the opposite direction to that ofthe arrow F, it suffices to exchange the characteristics of the washers4 and 6: according to this variant, therefore, not shown, the firstBelleville washer 4 is the assistance washer and the second Bellevillewasher 6 is the clamping washer. Here, in the clutch engaged position,the first washer 4 is at a distance from the annular abutment 32 and thesecond washer 6 is an abutment at the same time on the dishes 85 and 86on the bottom 80 of the cover 8; the annular abutment 32 here fulfillsthe role of declutching travel limitation.

In these figures there are visible the tangential tongues 9, and therivets 84 and 125 for fixing them, as well as the lugs 91, in radialprojection, on the thrust plate. In these figures, the device for takingup wear 90 is identical to that of FIG. 1.

According to the variant in FIG. 4, the second elastic washer 60, theone furthest away from the thrust plate 3, is the outer peripheral partof a diaphragm 206 extended inwards by a central part 207 divided intoradio fingers forming the declutching device; the diaphragm 206 ismounted articulated on the cover 8 in a conventional fashion by virtueof small columns 208, the clutch here being of the pushed type. Thesecond Belleville washer 60 is therefore the clamping washer and thefirst Belleville washer 40 the assistance washer.

In FIG. 4, the pieces or parts of the pieces identical to, or fulfillingthe same role as, those of the previous variant bear the samereferences.

Here, it is the second Belleville washer 60 which carries the actuator145, in the form of a radial appendage for actuating the control tongue135 of the elastic member 131 of the device for taking up wear 90; here,the non-return pawl 36 and tongue 135 are disposed roughly orthogonally;the support 112 and elastic member 131 are fixed to the cover 8 byrivets 200.

Here, the first washer 40 and second washer 60 are inclined in oppositedirections compared with the variant of FIGS. 2 and 3 and therefore bearon each other through their outer periphery. It is in the vicinity ofits median part that the first washer 40 cooperates with the stop zones114 of the sheet metal annulus of the ramp means 111; here, the saidannulus has a cylindrical axial shoulder 214 directed towards the bottomof the cover 8 and centring the first washer 40 by the inner peripherythereof; the transverse flank 232, bordered on one side by the stopzones 114 and one the other side by the axial shoulder 214, limits thetilting of the first washer 40 at the time of declutching; here, thesecond washer 60 is the clamping washer and the first washer 40 theassistance washer.

According to the variant depicted in FIG. 5, the second washer is also,as in the variant in FIG. 4, formed by the outer peripheral part of adiaphragm extended inwards by a central part divided into radial fingersby slots, and the clutch is of the pushed type. The first Bellevillewasher 40 is therefore the assistance washer and the second Bellevillewasher 60 the clamping washer.

Compared with the variant in FIG. 4, here force transmission means 305are provided and have an annular cylindrical skirt 306 to which there isattached internally a spring ring 307 interposed between the washers 40and 60 at their outer periphery; the skirt 306 centres the first washer40 with respect to the second washer 60, itself positioned by thediaphragm to which it belongs, the diaphragm being positionedconventionally by virtue of small columns fixed to the cover and notvisible in the Figure.

Here it is the skirt 306 which, at its external part on the cover side,carries the actuator 345, in the form of a radial appendage, in order toactuate the tongue 135 controlling the elastic member 131 of the devicefor taking up wear.

Here the sheet metal annulus of the ramp means 111, which carries theteeth 118, is centred at its inner periphery by a cylindrical step 303formed in the thrust plate 3; the said annulus has, towards its innerperiphery on the cover side, the stop zones 114 with which the firstwasher 4 cooperates through its inner periphery.

Naturally it is possible to use other types of declutching device 7,such as those described for example in FIGS. 3 and 4 of the Frenchpatent application filed on Apr. 7, 1997 under the number 97 04 213,whose corresponding description forms part of the present application.

According to the variant in FIG. 3 of this prior application, thedeclutching device comprises an annular disc carrying in its radiallymedian part, for example by riveting, the force transmission means 5;the clamping and assistance Belleville washers are placed on each sideof the annular disc; the latter also has at its outer periphery lugspassing through openings formed in the cylindrical peripheral skirt 82of the cover 8; these lugs are adapted to bear on an edge of theseopenings when the adjacent part of the inner periphery of the annulardisc is moved axially by the declutching stop 200, from right to left asseen in the figure, for the purpose of effecting the declutchingoperation, the clutch being shown as the pushed type.

It would of course be possible, as previously, by reversing the role ofthe washer, to produce as a variant a clutch of the pulled type having adeclutching device in the form of a disc, such as this one.

According to the variant depicted in FIG. 4 of this prior application,the declutching device comprises a disc having a central part in theform of fingers separated by slots, this central part extending aperipheral annular part. These fingers can be ribbed longitudinallycentrally. The annular part connects the fingers things together andconsists of a simple washer, optionally provided with blind radial slotsopening out towards the outside so that this washer exerts no load, or avery low load, axially.

As a variant, a low elasticity can be given to the peripheral part inorder to improve comfort at the pedal controlling the clutch releasebearing 200 and to exert a return action.

The disc is mounted so as to be articulated at the inner periphery ofthe bottom 80 of the cover 8, between two supports, one in the form of aspring ring, the other in the form of a dish on the bottom 80 of thecover 8, between which it is held by virtue of folded-over lugs on thecover; thus the disc is mounted so as to be articulated like a clutchdiaphragm. In this figure, as the clutch release bearing 200 isdepicted, the clutch is of the pulled type but naturally, as explainedabove, it could easily be transformed into a pushed clutch, byexchanging the washers.

What is claimed is:
 1. Friction clutch, having a clutch friction member (2) and a clutching mechanism having a cover (8) with a transversely oriented bottom (80) and fixing means (81) for fixing the clutching mechanism to a flywheel (1) driving in rotation, a thrust plate (3) having at the front a friction face (30) for cooperating with the clutch friction member (2), elastic tongues (9) for connecting the thrust plate (3) with the cover (8) with respect to rotation, with axial mobility, and, interposed between the back face (36) of the thrust plate (3) and the bottom (80) of the cover (8), on the one hand axially acting elastic clutching means (4, 60) axially forcing the thrust plate (8) in the opposite direction to the bottom (80) of the cover (8) and on the other hand a declutching device (7) for counteracting the action of the said elastic clutching means (4, 60) as required and moving the thrust plate in the direction of the bottom (80) of the cover (8) over a plate lifting distance, the clutching mechanism being equipped with a device for taking up wear (90) on at least one of the linings of the clutch friction member (2) and elastic assistance means (6, 40) for assisting the declutching force, elastic progressive action means (24) being mounted within the clutch friction member (2) and acting axially only on a travel of the thrust plate, characterised by the fact that the elastic assistance means (4) are mounted outside the clutch friction member (2) and the load/compression characteristic combining the load/compression characteristics of the elastic assistance (6, 40) and progressive action (24) means follows overall the load/compression characteristic of the axially acting elastic clutching means (4, 60).
 2. Clutch according to claim 1, characterised by the fact that the elastic clutching means (4, 60) and the elastic assistance means (6, 40) each consist of a Belleville washer, the two Belleville washers being mounted in series and placed axially between the thrust plate (3) and the bottom (80) of the cover (8).
 3. Clutch according to claim 2, characterised by the fact that a first Belleville washer (4) is referred to as the negative Belleville washer (4), its supplied load decreasing when the height of its truncated cone decreases, and a second Belleville washer (6) is referred to as the positive Belleville washer, its supplied load increasing when the height of its truncated cone decreases.
 4. Clutch according to claim 3, characterised by the fact that the thrust plate (3) has at its rear an abutment (32) situated radially below stop zones (114) in order to limit the inclination of the first Belleville washer (4).
 5. Mechanism according to claim 1, characterised by the fact that a force transmission means (5) are interposed between the inner peripheries of the first (4) and second (6) Belleville washers.
 6. Mechanism according to claim 2, characterised by the fact that the Belleville washers (4, 6) are maintained in contact with the force transmission means (5) by an elastic clamp (50), coming into engagement with the external faces of the Belleville washers (4, 6).
 7. Clutch according to claim 2, characterised by the fact that the declutching device (7) is annular in shape and the two Belleville washers (4, 6) are mounted in series between the thrust plate (3) and a manoeuvring stop (73) carried by the declutching device (7) which is mounted at its outer periphery so as to pivot on a primary stop (71) carried by the bottom (80) of the cover (8) radially above the manoeuvring stop (73), itself located radially above a secondary stop (72) carried by the bottom (80) of the cover (8).
 8. Clutch according to claim 7, characterised by the fact that, the device for taking up wear (90) having ramp means (111) with ramps disposed circumferentially and stop zones (114), the first Belleville washer (4) is in contact at its outer periphery with the stop zones (114), whilst the second Belleville washer (6) bears at its outer periphery on the manoeuvring stop (73), said washers (4, 6) being inclined in the opposite direction.
 9. Clutch according to claim 7, characterised by the fact that the declutching device (7) has a peripheral part (75) of annular shape extended by a main part (76) divided into radial fingers by slots.
 10. Clutch according to claim 9, characterised by the fact that the manoeuvring stop (73) is formed by stamping and is connected to the inner periphery of the annular peripheral part (75) of the declutching device (7) by a dish (74) directed axially in the opposite direction to the manoeuvring stop (73).
 11. Clutch according to claim 9, characterised by the fact that the peripheral part (75) of the declutching device (7) is offset axially with respect to its main part.
 12. Clutch according to claim 7, characterised by the fact that the primary stop (71) is offset axially with respect to the secondary stop (72).
 13. Clutch according to claim 5, characterised by the fact that the force transmission means (5) consist of a spring ring.
 14. Clutch according to claim 2, characterised by the fact that, the device for taking up wear (90) having ramp means (111) with ramps disposed circumferentially and stop zones (114), the first Belleville washer (4) is in contact with the stop zones (114), whilst the second Belleville washer (6) bears on the cover (8).
 15. Clutch according to claim 14, characterised by the fact that the first washer (4) is in contact through its outer periphery with the stop zones (114) whilst the second washer (6) bears through its outer periphery on the cover (8).
 16. Clutch according to claim 14, characterised by the fact that a force transmission means (5) is carried by the declutching device (7).
 17. Clutch according to claim 14, characterised by the fact that the first washer (40) is in contact through its median part with the stop zones (114) whilst the second washer (60) bears through its inner periphery on the cover (8).
 18. Clutch according to claim 14, characterised by the fact that the first washer (40) is in contact through its inner periphery with the stop zones (114) whilst the second washer (60) bears through its inner periphery on the cover (8).
 19. Clutch according to claim 14, characterised by the fact that the bottom (80) of the cover (8) carries an abutment (86) for limiting the inclination of the second Belleville washer (6).
 20. Clutch according to claim 14, characterised by the fact that the second elastic washer (60) is an outer peripheral part of a diaphragm (206) extended inwards by a central part (207) divided into radial fingers by slots.
 21. Clutch according to claim 14, characterised by the fact that the declutching device (7) comprises a transverse plate (41) carrying at its outer periphery the force transmission means (5) and connected by its inner periphery to a sleeve (42) mounted so as to slide axially.
 22. Clutch according to claim 14, characterised by the fact that the declutching device (7) comprises an annular disc (61) carrying in its radially median part the force transmission means (5) and having, at its outer periphery, lugs (62) passing through openings (18) formed in a cylindrical peripheral skirt (82) on the cover (8), the lugs (62) on the annular disc (61) being adapted to bear on an edge of these openings (18) when the adjacent part of its inner periphery of the annular disc (61) is moved axially.
 23. Mechanism according to claim 14, characterised by the fact that the declutching device (7) comprises a disc (75) having an annular part (72) extended towards the axis by a central part (76) divided into radial fingers by slots, the force transmission means (5) being placed at the outer periphery of said annular part (72), itself mounted so as to be articulated at the inner periphery of the bottom (80) of the cover (8).
 24. Clutch according to one of claim 1, characterised by the fact that the device for taking up wear (90) is actuated by the elastic clutching means (4, 60).
 25. Clutch according to one of claim 5, characterised by the fact that the device for taking up wear (90) is actuated by the force transmission means (305). 